LM431BCMX

Voltage Reference Overview

The LM431BCMX is a three-terminal adjustable precision shunt regulator manufactured by Fairchild Semiconductor. It functions as an active replacement for Zener diodes, offering programmable output voltage capability ranging from approximately 2.5 volts to 36 volts using two external resistors. The device features a typical dynamic output impedance of 0.2 ohms and supports a sink current range of 1.0 mA to 100 mA. It exhibits a full-range temperature coefficient of 50 ppm/°C and operates within a temperature range of -40°C to +85°C.

Voltage Reference Feature Summary

• Programmable output voltage settable between VREF (approx. 2.5V) and 36V via external resistors
• Low dynamic output impedance of 0.2 ohms typical
• Active output circuit provides sharp turn-on characteristic
• Temperature compensated for operation over the full rated operating temperature range

Voltage Reference Applications

• Replacement for Zener diodes in voltage reference applications
• Precision voltage regulation circuits
• Power supply feedback loops

Voltage Reference Procurement Notes

Verify the manufacturer designation on the component marking, as the LM431 family is produced by multiple vendors including Fairchild, National Semiconductor, and Texas Instruments. Confirm that the specific suffix matches the required package type and accuracy grade. Ensure compatibility with the system's thermal requirements and input voltage limits before integration.

Voltage Reference Selection Notes

Select this component when a low-cost, high-precision adjustable shunt regulator is required. The LM431BCMX offers tight initial accuracy suitable for general-purpose analog circuits. Consider the SOT-23-3 package constraints for PCB layout and ensure the external resistor network can handle the required power dissipation at maximum sink currents.

Voltage Reference Part Context

The LM431 series represents a standard industry solution for adjustable voltage references. Originally introduced by National Semiconductor, the design has been widely adopted and manufactured by various semiconductor companies under different part numbers. The LM431BCMX specifically denotes the Fairchild Semiconductor variant in a surface-mount package, maintaining the core electrical characteristics of the legacy through-hole TO-92 versions.

Voltage Reference Replacement Considerations

Direct pin-compatible substitutes include LM431BCM3X/NOPB (Texas Instruments) and LM431ACMLX (ON Semiconductor). Verify that alternative sources meet the same 50 ppm/°C temperature coefficient and 0.2 ohm dynamic impedance specifications to ensure circuit performance parity.